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Abstract:

A method for manufacturing a polishing head having an annular rigid ring;
a rubber film bonded to the rigid ring with uniform tension; a mid plate
joined to the rigid ring, forming a space together with the rubber film
and the rigid ring; and a mechanism for changing pressure of the space,
the method including performing a tensile test on the rubber film
according to JIS K6251 before bonding the rubber film to the rigid ring,
and selecting the rubber film having a value of 10 MPa or less of an
inclination obtained by a linear approximation of a stress-strain curve
within a strain value of 5%; and bonding the selected rubber film having
a value of 10 MPa or less of the inclination to the rigid ring to
manufacture the polishing head.

Claims:

1. A method for manufacturing a polishing head having at least: an annular
rigid ring; a rubber film bonded to the rigid ring with a uniform
tension; a mid plate joined to the rigid ring, the mid plate forming a
space together with the rubber film and the rigid ring; and a pressure
adjustment mechanism for changing pressure of the space, the polishing
head holding a back surface of a workpiece on a lower face portion of the
rubber film and polishing the workpiece by bringing a surface of the
workpiece into sliding contact with a polishing pad attached onto a turn
table, the method comprising the steps of:performing a tensile test on
the rubber film according to JIS K6251 before bonding the rubber film to
the rigid ring, and selecting the rubber film having a value of 10 MPa or
less of an inclination obtained by a linear approximation of a
stress-strain curve within a strain value of 5%; andbonding the selected
rubber film having a value of 10 MPa or less of the inclination to the
rigid ring to manufacture the polishing head.

2. The method for manufacturing a polishing head according to claim 1,
wherein the workpiece to be held is a silicon single crystal wafer having
a diameter of 300 mm or more.

3. A polishing apparatus having at least a polishing pad attached onto a
turn table, a polishing agent supply mechanism for supplying a polishing
agent onto the polishing pad, and a polishing head for holding a
workpiece, the polishing apparatus polishing a surface of the workpiece
while holding a back surface of the workpiece with the polishing head,
whereinthe polishing head has at least: an annular rigid ring; a rubber
film bonded to the rigid ring with a uniform tension; a mid plate joined
to the rigid ring, the mid plate forming a space together with the rubber
film and the rigid ring; and a pressure adjustment mechanism for changing
pressure of the space,the rubber film is formed by using a rubber
material having a value of 10 MPa or less of an inclination obtained by a
linear approximation of a stress-strain curve within a strain value of
5%, the stress-strain curve being obtained as a result of performing a
tensile test on the rubber film according to JIS K6251,the polishing pad
has a young's modulus of 3.5 MPa or less,the workpiece is polished by
bringing a surface of the workpiece into sliding contact with the
polishing pad attached onto the turn table with the pressure of the space
controlled by the pressure adjustment mechanism.

4. The polishing apparatus according to claim 3, wherein the workpiece to
be polished is a silicon single crystal wafer having a diameter of 300 mm
or more.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a method for manufacturing a
polishing head for holding a workpiece when a surface of the workpiece is
polished and a polishing apparatus provided with the polishing head
manufactured by the method, and more particularly to a method for
manufacturing a polishing head for holding the workpiece on a rubber film
and a polishing apparatus provided with the manufactured polishing head.

BACKGROUND ART

[0002]As an apparatus for polishing a surface of a workpiece such as a
silicon wafer, there are a single-side polishing apparatus, in which the
workpiece is polished by each side, and a double-side polishing
apparatus, in which the both sides of the workpiece are polished at the
same time.

[0003]For example as shown in FIG. 9, a common single-side polishing
apparatus comprises a turn table 88 onto which a polishing pad 89 is
attached, a polishing agent supply mechanism 90, a polishing head 82 and
the like. The polishing apparatus 81 polishes a workpiece W by holding
the workpiece W with the polishing head 82, supplying a polishing agent
onto the polishing pad 89 through the polishing agent supply mechanism
90, rotating the turn table 88 and the polishing head 82 respectively,
and bringing a surface of the workpiece W into sliding contact with the
polishing pad 89.

[0004]As a method for holding the workpiece in the polishing head, for
example, there is a method of attaching the workpiece onto a flat
disk-shaped plate through an adhesive such as a wax. Other than that,
particularly as a holding method of suppressing rise or sag on an outer
circumferential portion of the workpiece and of improving flatness of the
whole workpiece, there is a so-called rubber-chuck method in which a
workpiece holding portion is made of a rubber film, a pressurized fluid
such as air is poured into a back face of the rubber film, and the rubber
film is inflated by a uniform pressure so as to press the workpiece
toward the polishing pad (See Japanese Unexamined Patent Publication
(Kokai) No. H5-69310, for example).

[0005]An example of structure of a conventional polishing head by a
rubber-chuck method is schematically shown in FIG. 8. An essential part
of the polishing head 102 consists of an annular rigid ring 104 made of
SUS and the like, the rubber film 103 bonded to the rigid ring 104, and a
mid plate 105 joined to the rigid ring 104. A sealed space 106 is defined
by the rigid ring 104, the rubber film 103, and the mid plate 105. An
annular template 114 is provided concentrically with the rigid ring 104
in the periphery of a lower face portion of the rubber film 103. The
pressure of the space is adjusted, for example, by supplying a
pressurized fluid by a pressure adjustment mechanism 107 in a center of
the mid plate 105. A pressing means, not shown, for pressing the mid
plate 105 in the direction of the polishing pad 109 is provided.

[0006]As a material of the rubber film 103, there is a suggestion of
various rubber materials, such as a fluorinated rubber, a urethane
rubber, a silicon rubber, and an ethylene-propylene rubber, having a
rubber hardness ranging from 10 to 100, a tensile strength ranging from 3
to 20 MPa, and a tensile elongation ranging from 50 to 1000% in Japanese
Unexamined Patent publication (Kokai) No. 2005-7521.

[0007]With the polishing head 102 configured as above, the workpiece W is
held on a lower face portion of the rubber film 103 through a backing pad
113, an edge portion of the workpiece W is held with the template 114,
and the workpiece W is polished by bringing it into sliding contact with
the polishing pad 109 attached onto an upper face of the turn table 108
by pressing the mid plate 105.

DISCLOSURE OF INVENTION

[0008]Polishing the workpiece W by using the polishing head 102 in which
the workpiece W is held on the rubber film 103, as described above, may
improve flatness and polishing stock removal uniformity of the whole
workpiece W in some cases. However, there is a problem such that the
flatness and the polishing stock removal uniformity may decrease due to a
difference of material of the rubber film 103 or a difference of the
manufacturing lot even with regard to the same materials and thus stable
flatness of the workpiece W cannot be obtained.

[0009]The present invention was accomplished in view of the
above-explained problems, and its object is to provide a method for
manufacturing a polishing head and a polishing apparatus that can stably
obtain constant flatness in polishing of the workpiece W.

[0010]To achieve this object, the present invention provides a method for
manufacturing a polishing head having at least: an annular rigid ring; a
rubber film bonded to the rigid ring with a uniform tension; a mid plate
joined to the rigid ring, the mid plate forming a space together with the
rubber film and the rigid ring; and a pressure adjustment mechanism for
changing pressure of the space, the polishing head holding a back surface
of a workpiece on a lower face portion of the rubber film and polishing
the workpiece by bringing a surface of the workplace into sliding contact
with a polishing pad attached onto a turn table, the method comprising
the steps of: performing a tensile test on the rubber film according to
JIS K6251 before bonding the rubber film to the rigid ring, and selecting
the rubber film having a value of 10 MPa or less of an inclination
obtained by a linear approximation of a stress-strain curve within a
strain value of 5%; and bonding the selected rubber film having a value
of 10 MPa or less of the inclination to the rigid ring to manufacture the
polishing head.

[0011]In this manner, when the method comprises the steps of: performing a
tensile test on the rubber film according to JIS K6251 before bonding the
rubber film to the rigid ring, and selecting the rubber film having a
value of 10 MPa or less of an inclination obtained by a linear
approximation of a stress-strain curve within a strain value of 5%; and
bonding the selected rubber film having a value of 10 MPa or less of the
inclination to the rigid ring to manufacture the polishing head, the
polishing head can be manufactured which can suppress a variation in the
polishing stock removal uniformity that is generated between material
types of rubber film or material lots of the rubber film and which can
secure stably good flatness, in polishing of the workpiece.

[0012]In this case, the workpiece to be held can be a silicon single
crystal wafer having a diameter of 300 mm or more.

[0013]In this manner, even when the workpiece to be held is the silicon
single crystal wafer having a large diameter such as a diameter of 300 mm
or more, the polishing can be performed with more uniform pressing force
over the whole surface of the workpiece and thereby good flatness can be
secured, according to the present invention.

[0014]Furthermore, the present invention provides a polishing apparatus
having at least a polishing pad attached onto a turn table, a polishing
agent supply mechanism for supplying a polishing agent onto the polishing
pad, and a polishing head for holding a workpiece, the polishing
apparatus polishing a surface of the workpiece while holding a back
surface of the workpiece with the polishing head, wherein the polishing
head has at least: an annular rigid ring; a rubber film bonded to the
rigid ring with a uniform tension; a mid plate joined to the rigid ring,
the mid plate forming a space together with the rubber film and the rigid
ring; and a pressure adjustment mechanism for changing pressure of the
space, the rubber film is formed by using a rubber material having a
value of 10 MPa or less of an inclination obtained by a linear
approximation of a stress-strain curve within a strain value of 5%, the
stress-strain curve being obtained as a result of performing a tensile
test on the rubber film according to JIS K6251, the polishing pad has a
young's modulus of 3.5 MPa or less, the workpiece is polished by bringing
a surface of the workpiece into sliding contact with the polishing pad
attached onto the turn table with the pressure of the space controlled by
the pressure adjustment mechanism.

[0015]In this manner, when the polishing head has at least: an annular
rigid ring; a rubber film bonded to the rigid ring with a uniform
tension; a mid plate joined to the rigid ring, the mid plate forming a
space together with the rubber film and the rigid ring; and a pressure
adjustment mechanism for changing pressure of the space, the rubber film
is formed by using a rubber material having a value of 10 MPa or less of
an inclination obtained by a linear approximation of a stress-strain
curve within a strain value of 5%, the stress-strain curve being obtained
as a result of performing a tensile test on the rubber film according to
JIS K6251, the polishing pad has a young's modulus of 3.5 MPa or less,
the workpiece is polished by bringing a surface of the workpiece into
sliding contact with the polishing pad attached onto the turn table with
the pressure of the space controlled by the pressure adjustment
mechanism, a variation in the polishing stock removal uniformity which is
generated between material types of rubber film or material lots of the
rubber film can be suppressed, and the workpiece can be polished with
stably good flatness secured.

[0016]In this case, the workpiece to be polished can be a silicon single
crystal wafer having a diameter of 300 mm or more.

[0017]In this manner, even when the workpiece to be polished is the
silicon single crystal wafer having a large diameter such as a diameter
of 300 mm or more, the polishing can be performed with more uniform
pressing force over the whole surface of the workpiece and thereby good
flatness can be secured by holding it with the polishing head according
to the present invention to polish.

[0018]The method according to the present invention comprises the steps
of: performing a tensile test on the rubber film according to JIS K6251
before bonding the rubber film to the rigid ring, and selecting the
rubber film having a value of 10 MPa or less of an inclination obtained
by a linear approximation of a stress-strain curve within a strain value
of 5%; and bonding the selected rubber film having a value of 10 MPa or
less of the inclination to the rigid ring to manufacture the polishing
head. Thereby, the polishing head can be manufactured which can suppress
a variation in the polishing stock removal uniformity that is generated
between material types of rubber film or material lots of the rubber film
and which can secure stably good flatness, in polishing of the workpiece.

[0019]Moreover, the polishing apparatus according to the present invention
has at least the polishing pad attached onto the turn table, the
polishing agent supply mechanism for supplying the polishing agent onto
the polishing pad, and the polishing head manufactured by the
above-described method for manufacturing according to the present
invention, the polishing pad has a young's modulus of 3.5 MPa or less,
and the workpiece is polished by bringing a surface of the workpiece into
sliding contact with the polishing pad attached onto the turn table.
Thereby, a variation in the polishing stock removal uniformity that is
generated between material types of rubber film or material lots of the
rubber film can be suppressed, and the workpiece can be polished with
stably good flatness secured.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic view showing an example of the polishing
apparatus according to the present invention;

[0021]FIG. 2 are graphs showing an example of a stress-strain curve
obtained in the method for manufacturing a polishing head according to
the present invention, in which (A) shows the whole of the stress-strain
curve, and (B) shows the stress-strain curve within a strain value of 5%;

[0022]FIG. 3 are graphs showing the stress-strain curve in the step of
selecting the rubber film in Example 1, in which (A) shows the whole of
the stress-strain curve, and (B) shows the stress-strain curve within a
strain value of 5%;

[0023]FIG. 4 is a view showing the results of a value of an inclination
obtained by a linear approximation of the stress-strain curve within a
strain value of 5% in the step of selecting the rubber film in Example 1;

[0024]FIG. 5 is a view showing the results of the polishing pressure
distribution in Example 1 and Comparative Example.

[0025]FIG. 6 is a view showing the results of the polishing stock removal
uniformity in Example 1 and Comparative Example.

[0026]FIG. 7 is a view showing the results of the polishing stock removal
uniformity in Example 2 and Comparative Example.

[0027]FIG. 8 is a schematic view showing an example of a conventional
polishing head; and

[0028]FIG. 9 is a schematic view showing an example of a conventional
single-side polishing apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029]Hereinafter, an embodiment of the present invention will be
explained, but the present invention is not restricted thereto.

[0030]In the event that the workpiece is polished while holding the
workpiece on the rubber film by using a conventional polishing head,
there arises a problem such that a variation in polishing characteristics
occurs due to a difference in the type of the rubber, which is a material
of the rubber film of the polishing head, or due to a difference in the
lot even though there is no difference in the type, and thereby good
flatness cannot be obtained.

[0031]Moreover, such a variation in polishing characteristics is difficult
to be predicted based on physical properties such as the hardness of a
material lot of the rubber, which is a material of the rubber film, or
the tensile strength of the rubber.

[0032]In view of this, the present inventors keenly conducted experiments
and studies of the cause leading to the above-mentioned problem.

[0033]As a result, the present inventors found out the followings.

[0034]That is to say, good polishing stock removal uniformity can be
obtained by using a rubber material having a small stress for a fine
deformation of a strain of 5% or less, regardless of the type, the
hardness and the tensile strength of the rubber used as a material of the
rubber film. Specifically, when the rubber film having a small stress at
the time of finely deforming is used as the rubber film of the polishing
head to polish the workpiece, polishing can be performed with uniform
pressing force over the whole surface of the workpiece. In addition, when
the workpiece is polished by using the polishing head having a template,
pressure distribution in an outer circumferential portion of the
workpiece that is caused by a small difference between a height of a
lower end face of the template and a height of a lower end face of the
workpiece can be alleviated, and the polishing stock removal uniformity
can be consequently good.

[0035]Accordingly, the present inventors further keenly conducted
experiments and studies to quantify the stress at the time of finely
deforming of rubber materials to be used as the rubber film, investigated
polishing characteristics of these rubber materials, optimized, and
brought the present invention to completion.

[0036]FIG. 1 shows an example of the polishing head and the polishing
apparatus according to the present invention.

[0037]As shown in FIG. 1, the polishing apparatus 1 has the polishing head
2 and the turn table 8. The turn table 8 is of disk shape, and the
polishing pad 9 for polishing the workpiece W is attached onto its upper
face. A driving shaft 11 is vertically connected to an lower portion of
the turn table 8. The turn table 8 is configured to be rotated by a turn
table rotating motor (not shown) connected to an lower portion of the
driving shaft 11.

[0038]The polishing head 2 is provided above the turn table 8. The
polishing head 2 has the annular rigid ring 4, the rubber film 3 that is
bonded to the rigid ring 4 with a uniform tension and that has a flat
lower face, the mid plate 5 joined to the rigid ring 4, for example, with
bolts. A sealed space 6 is formed by the rigid ring 4, the rubber film 3
and the mid plate 5.

[0039]The polishing head 2 is rotatable about its axis.

[0040]Here, a material of the rigid ring 4 is not restricted in
particular. For example, it can be a rigid material such as SUS
(stainless steel). A material and a shape of the mid plate is also not
restricted in particular as long as the space 6 can be formed.

[0041]Moreover, a thickness of the rubber film 3 is not restricted in
particular. For example, it may be approximately 1 mm.

[0042]The rubber film used in the polishing head of the polishing
apparatus according to the present invention has the following
characteristics.

[0043]FIG. 2(A) shows an example of a stress-strain curve of the rubber
film, the stress-strain curve which is obtained as a result of performing
a tensile test according to JIS K6251. FIG. 2(B) is an enlarged graph of
a part within a strain value of 5% in the stress-strain curve shown in
FIG. 2(A). Here, a straight line obtained by performing the linear
approximation of the stress-strain curve within a strain value of 5%
using the least squares method, as shown in FIG. 2(B), is expressed as
stress=a×strain+b.

[0044]In the present invention, the rubber film is used in which a value
of the inclination a of this straight line is 10 MPa or less.

[0045]As shown in FIG. 1, the polishing apparatus has a polishing slurry
supply means 10 for supplying a polishing slurry to an upper part of the
turn table 8.

[0046]Moreover, an annular template 14 for holding an edge portion of the
workpiece W can be arranged in the periphery of the lower face portion of
the rubber film 3 to prevent the workpiece W from coming off during
polishing. In this case, the template 14 can be arranged so as to be
concentric with the rigid ring 4 and to project downward along an outer
circumferential portion of the lower face portion of the rubber film 3.

[0047]Here, the height of the lower end face of the template 14 can be the
same as the height of the lower end face of the held workpiece W or can
be such a height that the lower end face of the template 14 slightly
project downward, for example, by approximately 10 μm from the height
of the lower end face of the workpiece W.

[0048]The pressure distribution in the outer circumferential portion of
the workpiece can be alleviated by arranging the template 14 as described
above, thereby excessive polishing of the outer circumferential portion
of the workpiece can be prevented, and the polishing stock removal
uniformity of the workpiece can be improved.

[0049]Moreover, the template 14 can be configured such that its outer
diameter is larger than at least an inner diameter of the rigid ring 4
and its inner diameter is smaller than the inner diameter of the rigid
ring 4.

[0050]By this configuration, the polishing can be performed with more
uniform pressing force applied to the whole surface of the workpiece.

[0051]Here, it is preferable that a material of the template 14 is softer
than the workpiece W so as not to contaminate the workpiece W and to give
a scratch or an impression and is a high abrasion resistance material
that is hard to wear due to sliding contact with the polishing pad 9
during the polishing.

[0052]Moreover, as shown in FIG. 1, the polishing apparatus 1 has the
pressure adjustment mechanism 7 for changing the pressure of the space 6
of the polishing head 2.

[0053]A through-hole 12 for pressure adjustment communicating with the
pressure adjustment mechanism 7 is provided at the center of the mid
plate 5, and the pressure of the space 6 can be adjusted, for example, by
supplying a pressurized fluid by the pressure adjustment mechanism 7.

[0054]The polishing apparatus also has a means for pressing the mid plate
5 toward the polishing pad 9 (not shown).

[0055]In this case, a backing pad 13 can be attached to be provided on the
lower face of the rubber film 3. The backing pad 13 is made to contain
water so as to attach and to hold the workpiece W on a workpiece holding
face of the rubber film 3. Here, the backing pad 13 can be made of, for
example, foamed polyurethane. By providing the above-described backing
pad 13 and having it contain water, the workpiece W can be surely held by
surface tension of the water contained in the backing pad 13.

[0056]A soft polishing pad having a young's modulus of 3.5 MPa or less is
used as the polishing pad 9 attached onto an upper face of the turn table
8. When the polishing head 2 according to the present invention is used
in combination with the soft polishing pad 9 having a young's modulus of
3.5 MPa or less, contact pressure distribution between the workpiece W
and the polishing pad 9 can be more surely alleviated, and the polishing
stock removal uniformity of the workpiece W can be more surely improved.

[0057]It is to be noted that an embodiment of attaching the template 14
directly onto the rubber film 3 is shown in FIG. 1, but the present
invention does not exclude a case of attaching the template 14 onto the
rubber film 3 through the backing pad 13 and the like.

[0058]With the polishing apparatus 1 configured as described above, the
mid plate 5 is pressed toward the polishing pad 9 attached onto the turn
table 8 by the means for pressing the mid plate, not shown, and the
surface of the workpiece W is polished by bringing it into sliding
contact with the polishing pad 9 while the polishing agent is supplied
through the polishing agent supply mechanism 10. Here, the means for
pressing the mid plate is preferably able to press the mid plate 5 over
the whole surface with a uniform pressure, for example, by using an air
cylinder.

[0059]In this way, when the workpiece W is polished by using the polishing
apparatus 1 according to the present invention, the variation in the
polishing stock removal uniformity that is generated between the material
types of the rubber film 3 or the material lots of the rubber film 3 can
be suppressed, and the workpiece W can be polished with stably good
flatness secured.

[0060]In addition, the pressure distribution in the outer circumferential
portion of the workpiece W that is caused by a small difference between
the height of the lower end face of the template 14 and the height of the
lower end face of the workpiece W can be alleviated. The polishing can be
thereby performed while the pressing force applied to the workpiece W is
kept uniform over the whole surface, even though there are variations in
thicknesses of the workpiece W and the template 14 to a certain degree.
As a result, the workpiece W can be polished with good polishing stock
removal uniformity.

[0061]In this case, the workpiece to be polished can be a silicon single
crystal wafer having a diameter of 300 mm or more.

[0062]As described above, even when the workpiece to be polished is the
silicon single crystal wafer having a large diameter such as a diameter
of 300 mm or more, the polishing can be performed with more uniform
pressing force over the whole surface of the workpiece by holding it with
the polishing head according to the present invention to polish, and
thereby good flatness can be secured.

[0063]Next, the method for manufacturing a polishing head according to the
present invention will be explained.

[0064]For example as shown in FIG. 1, the polishing head manufactured by
the method for manufacturing according to the present invention is
configured to have at least: the annular rigid ring 4; the rubber film 3
bonded to the rigid ring 4 with a uniform tension; the mid plate 5 that
is joined to the rigid ring 4 and that forms the space 6 together with
the rubber film 3 and the rigid ring 4; and the pressure adjustment
mechanism 7 for changing the pressure of the space 6.

[0065]The method for manufacturing a polishing head according to the
present invention comprises at least the step of selecting the rubber
film 3 as follows.

[0066]First, the stress-strain curve as shown in FIG. 2(A) is obtained by
performing a tensile test on the rubber film 3 according to JIS K6251.
Then, from this stress-strain curve, the stress-strain curve within a
strain value of 5% is extracted as shown in FIG. 2(B), and a straight
line is obtained by performing the linear approximation of the extracted
curve using the least squares method. This straight line is expressed as
stress=a×strain+b.

[0067]Thereafter, the rubber film 3 having a value of 10 MPa or less of
the inclination a of the straight line is selected.

[0068]With the rubber film 3 selected as described above, it is bonded to
the rigid ring 4 with a uniform tension.

[0069]Here, the rubber film 3 can be selected at the stage of a rubber
material before forming the rubber film 3 itself, as long as it is
selected before bonding rubber film 3 to the rigid ring 4.

[0070]As described above, when the polishing head 2 is manufactured by
performing a tensile test on the rubber film 3 according to JIS K6251
before bonding the rubber film 3 to the rigid ring 4, selecting the
rubber film having a value of 10 MPa or less of the inclination obtained
by the linear approximation of the stress-strain curve within a strain
value of 5%, and bonding the selected rubber film 3 having a value of 10
MPa or less of the inclination to the rigid ring 4, the polishing head 2
can be manufactured which can suppress the variation in the polishing
stock removal uniformity that is generated between the material types of
the rubber film 3 or the material lots of the rubber film 3 and which can
secure stably good flatness, in polishing of the workpiece W.

[0071]Next, the mid plate 5 is joined to the rigid ring 4, and the space 6
is formed by the rigid ring 4, the mid plate 5 and the rubber film 3
bonded to the rigid ring 4. The pressure adjustment mechanism 7 is
arranged above the mid plate 5. These steps can be performed as with a
conventional method.

[0072]Here, the annular template 14 for holding the edge portion of the
workpiece W can be arranged in the periphery of the lower face portion of
the rubber film 3 to prevent the workpiece W from coming off during
polishing. In this case, the template 14 can be arranged so as to be
concentric with the rigid ring 4 and to project downward along the outer
circumferential portion of the lower face portion of the rubber film 3.

[0073]Here, the height of the lower end face of the template 14 can be the
same as the height of the lower end face of the workpiece W when the
workpiece is held or can be such a height that the lower end face of the
template 14 slightly project downward, for example, by approximately 10
μm from the height of the lower end face of the workpiece W.

[0074]The polishing head can alleviate excessive pressure distribution
applied to the outer circumferential portion of the workpiece by
arranging the template 14 as described above, and thereby can improve the
polishing stock removal uniformity of the workpiece.

[0075]Moreover, the template 14 can be configured such that its outer
diameter is larger than at least an inner diameter of the rigid ring 4
and its inner diameter is smaller than the inner diameter of the rigid
ring 4.

[0076]By this configuration, the polishing head can polish the workpiece
with more uniform pressing force applied to the whole surface of the
workpiece.

[0077]Here, it is preferable that the material of the template 14 is
softer than the workpiece W so as not to contaminate the workpiece W and
to give a scratch or an impression and is a high abrasion resistance
material that is hard to wear due to sliding contact with the polishing
pad 9 during the polishing.

[0078]In this case, the backing pad 13, for example, made of foamed
polyurethane can be attached to be provided on the lower face of the
rubber film 3. By providing the above-described backing pad 13 and having
it contain water, the polishing head can surely hold the workpiece W by
surface tension of the water contained in the backing pad 13.

[0079]In this case, the workpiece to be held can be the silicon single
crystal wafer having a diameter of 300 mm or more.

[0080]In this manner, even when the workpiece to be held is the silicon
single crystal wafer having a large diameter such as a diameter of 300 mm
or more, the polishing can be performed with more uniform pressing force
over the whole surface of the workpiece and thereby good flatness can be
secured, according to the present invention.

[0081]Hereinafter, the present invention will be explained in more detail
based on Example, but the present invention is not restricted thereto.

Example 1

[0082]The polishing heads as shown in FIG. 1 were manufactured by the
method for manufacturing according to the present invention. Silicon
single crystal wafers were polished with the polishing apparatus having
each manufactured polishing head, and the polishing stock removal
uniformity of each polished workpiece was evaluated.

[0083]First, in order to select the rubber film, there were prepared two
types of lot A and lot B of ethylene-propylene-diene rubber (EPDM) having
a hardness standard of 80°, which is a rubber hardness according
to JIS K6253, (hereinafter, referred to as EPDM 80° A and EPDM
80° B) and three types of silicone rubber having a hardness
standard of 70°, 80°, and 90° (hereinafter, referred
to as silicone 70°, silicone 80°, and silicone 90°),
as a rubber material of the rubber film. Tensile tests according to JIS
K6251 were performed on these 5 types of rubber materials, and the
stress-strain curves were measured each.

[0084]Table 1 shows the results of the tests. FIG. 3(A) shows the obtained
stress-strain curves. As shown in FIG. 3(B), the linear approximation was
performed, as stress=a×strain+b, using each stress-strain curve
within a strain value of 5% in FIG. 3(A), and a value of each inclination
a was calculated.

[0085]FIG. 4 shows the results of the values. As shown in FIG. 4, it was
revealed that even though the same type of rubber material was used, the
values of the inclination a were different due to the difference of the
lot, and in the rubber material of EPDM 80° B, silicone
70°, and silicone 80°, the values of the inclination a were
10 MPa or less.

[0086]After the rubber materials of the rubber films were selected as
described above, three polishing heads were manufactured using EPDM
80° B, silicone 70°, and silicone 80°, which had a
value of 10 MPa or less of the inclination a, by the following manner.

[0087]First, upper parts of the annular rigid rings that were made of SUS
and had an outer diameter of 360 mm were covered by the mid plates
respectively. The rubber films having a thickness of 1 mm were bonded to
the outer circumferences of the rigid rings with a uniform tension, using
three types of rubber materials (EPDM 80° B, silicone 70°,
and silicone 80°), which had a value of 10 MPa or less of the
inclination a.

[0088]The backing pad was attached to be provided on the workpiece holding
face of the rubber film of each polishing head. A commercial template
assembly, in which a template made of glass epoxy laminated sheet having
an outer diameter of 355 mm and an inner diameter of 302 mm was bonded,
was adhered to a surface of the backing pad by double-stick tape. In case
of the rubber film formed with silicone rubber, its surface was subjected
to coating processing with a thin polyurethane film having a thickness of
several μm for the purpose of improving capability for adhering to the
double-stick tape. Moreover, the commercial template assembly having a
thickness of 787 μm was used as the template so that the position of
the lower face of the template slightly project downward from the
position of the lower face of the workpiece.

[0089]With the polishing apparatus having the polishing head manufactured
by the method for manufacturing a polishing head according to the present
invention as shown in FIG. 1, silicon single crystal wafers having a
diameter of 300 mm and a thickness of 775 μm, as a workpiece W, were
polished. It is to be noted that both surfaces of the used silicon single
crystal wafers were subjected to the first polishing in advance, and its
edge portions were also subjected to polishing. The turn table having a
diameter of 800 mm was used. The polishing pad of the type of containing
urethane in a nonwoven fabric was used, and its young's modulus was 2.2
MPa, which is 3.5 MPa or less.

[0090]During the polishing, an alkaline solution containing colloidal
silica was used as the polishing agent, and the polishing head and the
turn table were rotated at 31, and 29 rpm respectively. A polishing load
(pressing force) of the workpiece W was set as 15 KPa. The polishing time
was 3 minutes.

[0091]The polishing stock removal uniformity and the polishing pressure
distribution during polishing of the workpiece polished as described
above were evaluated. It is to be noted that the polishing stock removal
uniformity is obtained by measuring the thickness of the workpiece before
and after polishing in a region excluding an outermost circumferential
portion 2 mm width, as a flatness quality area, with a flatness
measurement instrument in a diameter direction of the wafer and by taking
a difference in the thickness. It is represented by a formula of
polishing-stock-removal-uniformity (%)=(maximum polishing-stock-removal
in a diameter direction-minimum polishing-stock-removal in a diameter
direction)/average polishing-stock-removal in a diameter direction.

[0092]The polishing pressure distribution of the wafer in the range of 120
to 148 mm from its center in a diameter direction is shown in FIG. 5, the
wafer which was polished with the polishing head using EPDM 80° B
as the rubber material of the rubber film. The pressure distribution was
measured by converting the polishing stock removal at each position into
polishing-stock-removal/average
polishing-stock-removal×polishing-load (15 MPa) at each position.

[0093]As shown in FIG. 5, it was revealed that a decrease in pressure of
the outer circumferential portion of the workpiece W was more suppressed
and uniformity of the polishing pressure distribution was better in
comparison with the polishing head using the rubber film made of the
rubber material having a value of over 10 MPa of an inclination a, which
is used in later-explained Comparative Example.

[0095]As shown in FIG. 6, it was revealed that when polishing was
performed by the polishing apparatus having the polishing head using the
rubber film made of EPDM 80° B, silicone 70°, and silicone
80° respectively, the polishing stock removal uniformity was
improved in comparison with the result of the later-explained Comparative
Example, and that it was a good result of 10% or less.

[0096]Accordingly, it can be confirmed that the variation in the polishing
stock removal uniformity that is generated between material types of
rubber film or material lots of the rubber film can be suppressed and the
stably good flatness can be secured during polishing of the workpiece, by
using the polishing apparatus according to the present invention that has
the polishing head manufactured by the method for manufactured according
to the present invention.

Example 2

[0097]A polishing head using EPDM 80° B as the rubber film material
was manufactured as with Example 1. A silicon single crystal wafer was
polished with the polishing apparatus having the manufactured polishing
head and the polishing stock removal uniformity was evaluated as with
Example 1 except for using the polishing pad having a young's modulus of
3.2 MPa.

[0098]FIG. 7 shows the result of the polishing stock removal uniformity.
As shown in FIG. 7, it was revealed that the polishing stock removal
uniformity was improved in comparison with the result of the
later-explained Comparative Example, and that it was a good result of 10%
or less.

[0099]Moreover, as shown in FIG. 7, it was revealed that when the young's
modulus of the polishing pad was 3.5 MPa or less, the polishing stock
removal uniformity was a good result of 10% or less.

Comparative Example

[0100]Silicon single crystal wafers were polished in the same condition as
Example 1 except that the polishing heads were manufactured by using the
rubber material having a value of over 10 MPa of the inclination a
obtained, in Example 1, by the linear approximation was performed, as
stress=a×strain+b, using the stress-strain curve within a strain
value of 5%, that is, except for using EPDM 80° A and silicone
90° as the rubber film material, and the polishing stock removal
uniformity and the polishing pressure distribution during the polishing
of each polished wafer were evaluated.

[0101]FIG. 5 shows the results of the polishing pressure distribution. As
shown in FIG. 5, it was revealed that the decrease in pressure of the
outer circumferential portion of the workpiece was more remarkable and
uniformity of the polishing pressure distribution was decreased in
comparison with the result of Example 1 in which the rubber film having a
value of 10 MPa or less of the inclination a was selected.

[0102]FIG. 6 shows the results of the polishing stock removal uniformity.
As shown in FIG. 6, it was revealed that the polishing stock removal
uniformity was worse than the results of Example 1.

[0103]Accordingly, it was confirmed that when the workpiece was polished
with a conventional polishing apparatus, the variation in the polishing
stock removal uniformity occurred and stable flatness of the workpiece
was not obtained due to the differences of the rubber film material and
of the manufacturing lot even with regard to the same materials.

[0104]Next, a silicon single crystal wafer was polished in the same
condition as Example 2 except for using the polishing pad having a
young's modulus of 4.5 MPa, and the polishing stock removal uniformity of
the polished wafer was evaluated.

[0105]FIG. 7 shows the result of the polishing stock removal uniformity.
As shown in FIG. 7, it was revealed that the polishing stock removal
uniformity was worse than the result of Example 2. That is to say, the
polishing head according to the present invention that selects the rubber
film having a value of 10 MPa or less of the inclination obtained by the
linear approximation of the stress-strain curve within a strain value of
5% enables the polishing stock removal uniformity to be improved, and
when the polishing apparatus is provided with the polishing head to
polish, the polishing pad attached onto the turn table needs to have a
young's modulus of 3.5 MPa or less.

[0106]It is to be noted that the present invention is not restricted to
the foregoing embodiment. The embodiment is just an exemplification, and
any examples that have substantially the same feature and demonstrate the
same functions and effects as those in the technical concept described in
claims of the present invention are included in the technical scope of
the present invention.

[0107]For example, the polishing head manufactured by the method for
manufacturing according to the present invention is not restricted to an
embodiment shown in FIG. 1, and for example, a shape and the like of the
mid plate may be appropriately designed.

[0108]Moreover, the structure of the polishing apparatus is also not
restricted to the embodiment shown in FIG. 1, and for example, the
polishing apparatus can be provided with a plurality of the polishing
head manufactured by the method for manufacturing according to the
present invention.